Francisella tularensis is a facultative, intracellular, Gram-negative bacterium that is the causative agent of tularemia, a severe and potentially lethal zoonotic disease. This NIAID Category A pathogen has been recognized for several decades as a potential threat to public health as a bioweapon for a number of reasons. These include its ability to infect via multiple routes, the very low infectious dose required to cause serious disease, the acquisition by aerosol exposure of respiratory tularemia, the most debilitating and lethal fond of the disease, and the ease with which aerosolized organisms could be widely disseminated. In light of recent concerns about bioterrorism, the development of new therapies to defend against the use of F. tularensis as a biological weapon is a priority.
Autophagy is a mechanism of cellular homeostasis in which cytoplasmic material is sequestered in characteristic vacuoles called autophagosomes and then delivered to lysosomes for degradation. This evolutionarily conserved process provides for the recycling of long-lived cytosolic proteins to fulfill cellular needs for energy and survival in response to environmental stress or nutrient deprivation, and for the removal of excess or damaged organelles which may serve to protect cells from apoptosis. Recent studies have established a role for autophagy in cellular defense against intracellular pathogens including bacteria, such as Mycobacterium tuberculosis, Streptococcus pyogenes, Shigella spp. and Salmonella typhimurium, as well as viruses and protozoa. The execution of autophagy is regulated by upstream signal transduction systems that are influenced by largely physiological factors such as nutrient status, growth factors/cytokines, and hypoxia. The pharmacological induction of autophagy represents an intriguing and unexploited therapeutic strategy in which this effector of innate immunity would be triggered or amplified to defend against intracellular pathogens.
OSU-03012 (formula XV), a PDK-1/Akt signaling inhibitor, is one of many distinct classes of molecularly targeted agents developed by the inventors. OSU-03012 was derived through structure-based optimization of the COX-2 inhibitor, celecoxib, with regard to PDK-1 activity. Based in part on the novelty of its molecular target and its importance in cancer cell survival, the compound entered into preclinical evaluation through the NCI RAID program. Investigation of OSU-03012 revealed that it induces autophagy with a sub-μM IC50. This point is noteworthy for two reasons. First, concentrations in this range are clearly attainable in the in vivo preclinical and clinical settings. Second, this IC50 for autophagy induction is quite a bit lower than that for inhibition of PDK-1 activity (˜5 μM), which suggests a mechanism distinct from inhibition of PDK-1/Akt signaling.